What is the most dramatic way of increasing a speaker's Bass and Low mid?

There are tons of interesting ideas on this thread.

But I'm going to reiterate: you can't fix what you can't measure.

Get a USB measurement mic from Parts Express.  Use it, and post a FR plot.

Let's see exactly what we're dealing with.  Then you'll also see what your improvements do.  It's possible that relatively minor adjustments in speaker placement could yield the improvements you're looking for.

Ears are great and all, but the placebo effect is all too real - I worked in Pharma QA, and it is frankly terrifying.  It is only now, more than 20 years later, that studies suggest Prozac MIGHT work better than a placebo, for example.  The analogy to various audio tweaks is left as an exercise..

@Fraterperdurabo   you right for 100%  The majority interesting ideas
is placebo effect. Get measuring tools  is very helpful. 

I'm an electronics technician who is very accustomed to working with all kinds of measuring tools, but the only thing that can measure "high end" audio is a pair of keen ears.

The people who don't have them wouldn't understand that fact.

I am  electronics engineer with big experience   to speakers building
and have currently selling speakers.   i say--  you have to use  the both--
you ears  because the ears is very precise and measuring tools.
measuring microphone also very important, see all stereophile  
revue , they make measuring test for all famous brand,  i dont think
you can recommend John dont do it   

I'm going to have room treatments done, that will most certainly require professional measuring equipment, and someone who knows how to use it.